Mesoscale Discussion 0001
   NWS Storm Prediction Center Norman OK
   0738 PM CST Thu Dec 31 2020

   Areas affected...Portions of western into northwest
   Texas...southwestern into central Oklahoma

   Concerning...Winter mixed precipitation 

   Valid 010138Z - 010745Z

   SUMMARY...A wintry mix is expected to continue across portions of
   southwest Texas into central Oklahoma. Heavier snow will most likely
   occur across portions of western Texas, while freezing rain,
   occasionally mixed with sleet, is expected to be the predominant
   winter weather hazard across portions of central Oklahoma over the
   next several hours.

   DISCUSSION...An occluding upper low across southwest TX continues to
   gradually pivot northeastward, with an 850 mb low remaining nearly
   stationary across portions of northern TX as of 01Z. Deep-layer
   cyclonic flow supports a 925-700 mb warm conveyor belt continuing a
   supply of moisture across portions of Oklahoma into northwest Texas,
   but with up to 5C temperatures (mainly around 850 mb per 00Z OUN
   observed sounding). The warmer temperatures in the sfc-850 mb layer
   have inhibited greater winter weather precipitation rates across
   portions of OK so far. However, given the southward advection of
   relatively drier surface air (27-30 F dewpoints) from farther north,
   temperatures may drop a few degrees over the next several hours.
   Occasional instances of freezing rain have been noted from OKC to
   SPS over the past couple of hours, with additional freezing rain and
   sleet possible overnight as low-level temperatures continue to
   gradually cool. 

   Farther southwest, the 00Z MAF sounding shows a sub-freezing
   troposphere, with METAR observations to the east showing
   sub-freezing surface temperatures and heavier snowfall (as also
   supported by KSJT dual-polarimetric radar data) over the past few
   hours. An 800-1000 m deep, nearly saturated dendritic growth zone
   suggests that heavier snow (perhaps a brief instance or two of 1
   inch/hr rates) should continue for at least a few more hours, until
   the upper-low pivots farther northward out of the area. Thereafter,
   heavier snow may move into southwestern and central Oklahoma by
   07-08Z per latest HRRR guidance.

   ..Squitieri/Bunting.. 01/01/2021

   ...Please see www.spc.noaa.gov for graphic product...

   ATTN...WFO...TSA...FWD...OUN...SJT...LUB...MAF...

   LAT...LON   31880234 32290219 32860183 33640088 34389938 35079848
               35839768 36199685 35949604 35699603 35359609 34919637
               33999730 33489772 32809822 31709889 31129907 30739966
               30840045 31070113 31880234